The problem MIGHT be that you are on Win7.
The 64bit version of WBFS 4.0 is buggy, and the Fusion chip isn't always happy with the way the software puts the isos on the SD card.
Try again with the 32bit version on win xp (and be sure to only add ONE game at a time, again, another bug in the software causes bad transfers if you add more then one game to the SD card).

If you know how to install and run 32bit version on Windows 7 then that can help a lot if you dont have an XP 32 or Windows 7 32bit. Google it and you will find lot of site about how to run 32bit software on 64bit OS